1. Field of the Invention
The present invention relates to a pore forming material for a porous body, a manufacturing method of the pore forming material for a porous body, a manufacturing method of a porous body, a porous body, and a honeycomb structural body.
2. Discussion of the Background
In recent years, particulates, such as soot and the like, contained in exhaust gases that are discharged from internal combustion engines of vehicles, such as buses, trucks and the like, and construction machines and the like, have raised serious problems as those particulates are harmful to the environment and the human body.
In order to solve these problems, there have been proposed various honeycomb structural bodies made of porous ceramics, which serve as filters for collecting particulates in exhaust gases to purify the exhaust gases.
With respect to a method for manufacturing a porous body to be used for honeycomb structural bodies of this type, for example, a method has been proposed in which: polymer particles (pore forming material for a porous body) having a pore forming function are mixed in an aggregate made of ceramics, metal and the like, and the resulting product is formed, dried, degreased and fired so that a porous body is manufactured (for example, see JP-A 2003-10617). In such a manufacturing method, almost all the polymer particles are burned to be removed during the degreasing process so that portions that have been occupied by the polymer particles are allowed to form pores; thus, after the firing process, a porous body having the resulting pores is formed.
Moreover, in the honeycomb structural body made of a porous body, the porosity of the porous body forms a very important factor that determines the performance of a filter, and there have been strong demands for a filter having a great porosity from the viewpoints of an increased supported amount of catalyst, the collecting efficiency of fine particles, the pressure loss and the collecting time.
Therefore, in order to manufacture a porous body having a great porosity by using the above-mentioned method, it is necessary to increase the content of polymer particles. However, in this case, an abrupt heat generating reaction is exerted upon burning the polymer particles in the drying, degreasing and firing processes to cause a portion which locally has high temperatures.
Furthermore, in the case where the polymer particles are formed into porous bodies (with a lower density) in an attempt to reduce the content of the polymer particles, the polymer particles are squashed upon applying a high pressure thereto during the forming process.
The contents of JP-A 2003-10617 are incorporated herein by reference in their entirety.